Transmission apparatus, transmission method, and wireless communication system for orthogonal cover code (occ) generation and occ mapping

ABSTRACT

A base station which performs Multiple Input Multiple Output (MIMO) transmission. A processor configured to generate reference signals by spreading with four groups of orthogonal code sequences, each group of orthogonal code sequences including four orthogonal sequences, wherein the orthogonal code sequences correspond to transmission layers and each of the orthogonal code sequences has a length of four, and a transmit circuit configured to transmit the reference signals. The four groups include a first group where the orthogonal code sequences are Walsh code sequences, a second group where the orthogonal code sequences are represented by mirroring of the orthogonal code sequences in the first group, a third group where the orthogonal code sequences are represented by cyclic shifts of the orthogonal code sequences in the first group, a fourth group where the orthogonal code sequences are represented by mirroring of the orthogonal code sequences in the third group.

The present application is a continuation application of the U.S. patentapplication Ser. No. 14/636,533 filed Mar. 3, 2015, which is acontinuation U.S. patent application Ser. No. 13/618,302, filed Sep. 14,2012, now U.S. Pat. No. 9,001,639, issued Apr. 7, 2015, which is acontinuation of international patent application No. PCT/CN2010/071532,filed Apr. 2, 2010, the entire contents of each are wholly incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to transmission technology in the wirelesscommunication system, and in particular to an orthogonal cover codegeneration apparatus and method and an orthogonal cover code mappingapparatus and method in a wireless communication system such as anLTE/LTE-A system.

BACKGROUND OF THE INVENTION

The next-generation wireless communication system LTE-A (Long TermEvolution-Advanced) of 3 GPP requires providing a peak rate of 1 Gps anda peak spectrum efficiency of 30 bps/Hz in the downlink. This bringschallenge to the transmission scheme in the physical layer of thesystem. A multi-antenna MIMO (Multiple Input Multiple Output) system isable to support parallel data flow sending thereby greatly increasingthe system throughput. Typically, the independent forward errorcorrection encoding is firstly performed on the parallel data flow inthe multi-antenna transmission, and then the encoded code words aremapped into the corresponding data transmission layer. In onetransmission, the number of all the layers supported by the system isalso referred to as a Rank of this transmission. The process oftransforming data in each layer into data on each physical antenna isreferred to as a pre-encoding process for a signal. LTE-A Rel-10supports a pre-encoding technology with maximum Rank of 8.

The sending terminal should transmit pilot sequences used for channelestimation, namely demodulation reference signals (DMRSs), for thereceiving terminal to perform MIMO decoding and related demodulation.The design of DMRSs should satisfy that DMRSs corresponding to each datatransmission layer are mutually orthogonal, i.e. ensure that there is nointerference between equivalent channels of pre-encoded channels ofrespective sending antennas. In a Rel-10 system, DMRSs corresponding toeach data transmission layer are distinguished in the manner offrequency division multiplexing (FDM) and/or code division multiplexing(CDM). The code division multiplexing is implemented by spreadingsequences whose correlation is ideal with orthogonal cover codesequences. The orthogonal cover code sequences usually employ Walsh Codesequences or Discrete Flourier Transform sequences.

If the orthogonal cover code sequences are mapped in the time domain,i.e. spread in the time domain, it is usually assumed that the channelsin the physical resources corresponding to the cover code sequences areidentical. Assuming that a spreading factor of a spreading sequence isM, the channel response of the M OFDM symbols are considered to beidentical. This assumption is true in the low speed environment.However, with the increasing moving speed of a mobile station,variations of the channel response of the M OFDM symbols increase andthe orthogonality of the spreading codes are destroyed, leading tomutual interference between respective data transmission layers and thusreducing the accuracy of the channel estimation.

Moreover, in the Rel-10 system, DMRSs are subjected to the samepre-encoding process as that for data and are mapped onto each sendingantenna. The pre-encoding process performs linear superposition on theDMRSs corresponding to each of the code division multiplexed datatransmission layers. If the DMRSs corresponding to the M datatransmission layers are superposed in the same direction, a signal withamplitude of M is gotten; and if the DMRSs corresponding to the M datatransmission layers are superposed in the opposite direction, they aremutually canceled out and a signal with amplitude of 0 is gotten. Ifsuch power imbalance of each of the sending antennas occurs in theentire frequency bandwidth, the efficiency of the transmission power maybe reduced apparently.

The reference documents of the present invention are listed in thefollowing, which are incorporated herein by reference as if they aredescribed in detail in the present description.

1. [Patent Document 1]: Ishii Hiroyuki, Higuchi Kenichi, Base stationapparatus, user apparatus and method used in mobile communication system(US 20100034077 A1);

2. [Patent Document 2]: Hooli Kari, Pajukoski Ka, et al., Method,apparatuses, system and related computer product for resource allocation(WO 2009056464 A1);

3. [Patent Document 3]: Kim Hak Seong, Yun Young Woo, et al., Method oftransmitting scheduling reference signal (US 20100008333 A1);

4. [Patent Document 4]: Che Xiangguang, Guo Chunyan, et al., Variabletransmission structure for reference signals in uplink messages (WO2009022293 A2);

5. [Patent Document 5]: Cho Joon-young, Zhang Jianzhong, et al.,Apparatus and method for allocating code resource to uplink ACK/NACKchannels in a cellular wireless communication system (US 2009046646 A1);

6. [Patent Document 6]: Yang Yunsong, Kwon Younghoon, System and methodfor adaptively controlling feedback information (US 20090209264 A1); and

7. [Patent Document 7]: Pajukoski Kari P, Tiirola Esa, Providingimproved scheduling request signaling with ACK/NACK or CQI (US20090100917).

SUMMARY OF THE INVENTION

Hereinafter, a brief summarization about the present invention is given,so as to provide basic understanding of some aspects of the presentinvention. However, it should be understood that this summarization isnot an exhaustive summarization about the present invention. It does notintend to be used to either determine a key or important part of thepresent invention or define the scope of the present invention. Itsobject is only to give some concepts about the present invention in asimplified form and hereby acts as a preamble of more detaileddescriptions which will be presented later.

In view of the above mentioned situation in the prior art, the object ofthe present invention is to provide an orthogonal cover code generationapparatus and method and an orthogonal cover code mapping apparatus andmethod, which may solve one or more of the problems in the prior art.

In order to achieve the above mentioned object, according to one aspectof the present invention, there is provided an orthogonal cover codegeneration apparatus, including: a first orthogonal cover code sequencegroup generation means for generating a first group of orthogonal covercode sequences C₁ represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2) ,. . . C_(n, 1)(M)], which satisfy that any adjacent truncated sub covercode sequences [C_(2J−1, 1)(2m−1), C_(2J−1, 1)(2m)] and[C_(2j, 1)(2m−1), C_(2j, 1)(2m)] are also mutually orthogonal, wherein nis an index of N orthogonal cover code sequences included in the firstgroup of orthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2; asecond orthogonal cover code sequence group generation means forperforming column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂ ; a third orthogonal cover code sequence group generationmeans for performing cyclic shift processing of column vectors on thefirst group of orthogonal cover code sequences, so as to generate athird group of orthogonal cover code sequences C₃; and a fourthorthogonal cover code sequence group generation means for performingcolumn mirroring on the third group of orthogonal cover code sequences,so as to generate a fourth group of orthogonal cover code sequences C₄.

According to another aspect of the present invention, there is furtherprovided an orthogonal cover code mapping apparatus, including: theorthogonal cover code generation apparatus mentioned above forgenerating multiple groups of orthogonal cover code sequences, whereinthe multiple groups of orthogonal cover code sequences comprise at leastthe first to fourth groups of orthogonal cover code sequences; and aspreading means for spreading pilot sequences with the multiple groupsof orthogonal cover code sequences according to a predetermined mappingrule.

According to another aspect of the present invention, there is furtherprovided an orthogonal cover code generation method, including: a firstorthogonal cover code sequence group generation step of generating afirst group of orthogonal cover code sequences C₁ represented by amatrix of [C_(n, 1)(1), C_(n, 1)(2), . . . C_(n, 1)(M)], which satisfythat any adjacent truncated sub cover code sequences [C_(2j−1, 1)(2m−1),C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1), C_(2j, 1)(2m)] are also mutuallyorthogonal, wherein n is an index of N orthogonal cover code sequencesincluded in the first group of orthogonal cover code sequences, M is aspreading factor of the orthogonal cover code sequence as a spreadingsequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integersatisfying 1≦m≦M/2; a second orthogonal cover code sequence groupgeneration step of performing column mirroring on the first group oforthogonal cover code sequences, so as to generate a second group oforthogonal cover code sequences C₂ ; a third orthogonal cover codesequence group generation step of performing cyclic shift processing ofcolumn vectors on the first group of orthogonal cover code sequences, soas to generate a third group of orthogonal cover code sequences C₃; anda fourth orthogonal cover code sequence group generation step ofperforming column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄.

According to another aspect of the present invention, there is furtherprovided an orthogonal cover code mapping method, including: anorthogonal cover code generation step of generating, according to theorthogonal cover code generation method mentioned above, multiple groupsof orthogonal cover code sequences, wherein the multiple groups oforthogonal cover code sequences comprise at least the first to fourthgroups of orthogonal cover code sequences; and a spreading step ofspreading pilot sequences with the multiple groups of orthogonal covercode sequences according to a predetermined mapping rule.

According to another aspect of the present invention, there is furtherprovided a computer program product for realizing the orthogonal covercode generation method and/or the orthogonal cover code mapping methodmentioned above.

According to another aspect of the present invention, there is furtherprovided a computer readable medium with the computer program codes forrealizing the orthogonal cover code generation method and/or theorthogonal cover code mapping method mentioned above recorded thereon.

According to another aspect of the present invention, there is furtherprovided a wireless communication system including a transmissionapparatus and a reception apparatus, wherein the transmission apparatusincludes: a first orthogonal cover code sequence group generation meansfor generating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, wherein n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2; asecond orthogonal cover code sequence group generation means forperforming column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂; a third orthogonal cover code sequence group generationmeans for performing cyclic shift processing of column vectors on thefirst group of orthogonal cover code sequences, so as to generate athird group of orthogonal cover code sequences C₃; and a fourthorthogonal cover code sequence group generation means for performingcolumn mirroring on the third group of orthogonal cover code sequences,so as to generate a fourth group of orthogonal cover code sequences C₄,and wherein the reception apparatus includes a reception means forreceiving the spread pilot sequences from the transmission apparatus.

According to another aspect of the present invention, there is furtherprovided a base station including the orthogonal cover code generationapparatus mentioned above.

According to another aspect of the present invention, there is furtherprovided a mobile station including the orthogonal cover code generationapparatus mentioned above.

According to another aspect of the present invention, there is furtherprovided a method in a wireless communication system including atransmission apparatus and a reception apparatus, the method comprising:at the transmitting apparatus, generating a first group of orthogonalcover code sequences C₁ represented by a matrix of [C_(n, 1)(1),C_(n, 1)(2), . . . C_(n, 1)(M)], which satisfy that any adjacenttruncated sub cover code sequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)]and [C_(2j, 1)(2m−1), C_(2j, 1)(2m)] are also mutually orthogonal,wherein n is an index of N orthogonal cover code sequences included inthe first group of orthogonal cover code sequences, M is a spreadingfactor of the orthogonal cover code sequence as a spreading sequence,N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying1≦m≦M/2; performing column mirroring on the first group of orthogonalcover code sequences, so as to generate a second group of orthogonalcover code sequences C₂; performing cyclic shift processing of columnvectors on the first group of orthogonal cover code sequences, so as togenerate a third group of orthogonal cover code sequences C₃; andperforming column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄, and at the reception apparatus, receiving the spread pilotsequences from the transmission apparatus.

According to the above mentioned technique scheme of the presentinvention, by performing column mirroring and cyclic shift processing ofcolumn vectors on a group of orthogonal cover code sequences, multiplegroups of orthogonal cover code sequences are generated to randomizeDMRS signals, so as to overcome the problems of imbalanced transmissionpower due to pre-encoding. Moreover, the orthogonal cover code sequencesgenerated according to the present invention not only ensureorthogonality in one dimension, such as time domain spreading, but alsoprovide orthogonality in time-frequency two-dimensions, thereby reducingthe effect of the moving speed of a mobile station on the orthogonalityof DMRSs of different data transmission layers and thus to improve therobustness of channel estimation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood with reference to thedetailed description given in conjunction with the accompany drawings asfollows. Throughout all the accompany drawings, identical or similarreference numerals are used to represent identical or similarcomponents. The accompany drawings together with the following detaileddescription are contained in the present specification and form part ofthe specification, for further illustrating the preferable embodimentsof the present invention and explaining the principles and advantages ofthe present invention by way of example, in which:

FIG. 1 shows a flow chart of an orthogonal cover code generation methodaccording to an embodiment of the present invention;

FIG. 2 shows an example diagram of four groups of orthogonal cover codesequences generated according to the present invention.

FIG. 3 shows a flow chart of an orthogonal cover code mapping methodaccording to an embodiment of the present invention;

FIG. 4 shows a schematic view of downlink DMRSs in the Rel-10 system;

FIG. 5 shows a schematic view of mapping the four groups of orthogonalcover code sequences generated according to the present invention intothe downlink DMRS resources in the Rel-10 system;

FIG. 6 shows a schematic view of power distribution of mapping thepre-encoded four groups of orthogonal cover code sequences generatedaccording to the present invention onto a first sending antenna;

FIG. 7 shows a schematic view of the orthogonality in time-frequencytwo-dimensions satisfied when the four groups of orthogonal cover codesequences generated according to the present invention are mapped intothe downlink DMRSs in the Rel-10 system;

FIG. 8 shows a structural block diagram of an orthogonal cover codegeneration apparatus according to an embodiment of the presentinvention;

FIG. 9 shows a structural block diagram of an orthogonal cover codemapping apparatus according to an embodiment of the present invention;

FIG. 10 shows a structural block diagram of a wireless communicationsystem according to an embodiment of the present invention;

FIG. 11 shows a structural block diagram of a base station according toan embodiment of the present invention; and

FIG. 12 shows a structural block diagram of a mobile station accordingto an embodiment of the present invention.

The skilled in the art should understand that, the elements in theaccompany drawings are only shown for the sake of simplicity and claritybut not necessarily drawn to scale. For example, sizes of some elementsin the accompany drawings may be enlarged relative to other elements soas to help to improve the understanding of the embodiments of presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention will be described belowin conjunction with the accompanying drawings. For the sake ofsimplicity and clarity, not all of the features of practicalimplementations are described in the specification. However, it shouldbe understood that during developing any of such practicalimplementations, many implementation-specific decisions should be madein order to achieve a specific object of a developer, for example toconform to the limitations relevant to a system or business, and thoselimitations may vary with different implementations. Moreover, it shouldalso be understood that although the development work may be verycomplicated and time consuming but may simply be a routine task forthose skilled in the art benefiting from this disclosure.

It shall further be noted that only those device structures and/orprocess steps closely relevant to the solutions of the invention areillustrated in the drawings while other details less relevant to theinvention are omitted so as not to obscure the invention due to thoseunnecessary details.

Referring to the accompany drawings, the orthogonal cover codegeneration method and orthogonal cover code mapping method according toembodiments of the present invention are to be described in detail asfollows.

FIG. 1 shows a flow chart of an orthogonal cover code generation methodaccording to an embodiment of the present invention.

Firstly, in step S110, a first group of orthogonal cover code sequencesC₁ is generated. The first group of orthogonal cover code sequences arerepresented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, where n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2.Preferably, the first group of orthogonal cover code sequences C₁ may beWalsh Code sequences or Flourier Transform sequences.

Next, in step S120, column mirroring is performed on the first group oforthogonal cover code sequences, so as to generate a second group oforthogonal cover code sequences C₂.

Next, in step S130, cyclic shift processing of column vectors isperformed on the first group of orthogonal cover code sequences, so asto generate a third group of orthogonal cover code sequences C₃.

Finally, in step S140, column mirroring is performed on the third groupof orthogonal cover code sequences, so as to generate a fourth group oforthogonal cover code sequences C₄.

Preferably, the first to fourth groups of orthogonal cover codesequences are respectively represented by a matrix C_(i)=[C_(n, 1)(1),C_(n, 1)(2), . . . C_(n, 1)(M)], where i is an index of each group oforthogonal cover code sequences, the first to fourth groups oforthogonal cover code sequences satisfy that the column vectors of eachgroup of orthogonal cover code sequences have different column numbersin a matrix of each group of orthogonal cover code sequences, and {tildeover (C)}_(n,k) ^(l)=[C_(n,2k−1)(2l−1), C_(n,2k−1)(2l), C_(n,2k)(2l−1),C_(n,2k)(2l)] composed of two adjacent groups of orthogonal cover codesequences C_(2k−1) and C_(2k) satisfy that {tilde over (C)}_(n1,k) ^(l)and {tilde over (C)}_(n2,k) ^(l) are mutually orthogonal, where k=1 or2, 1 is an integer satisfying 1≦l≦M/2, n1 is an integer satisfying1≦n1≦N, n2 is an integer satisfying 1≦n2≦N, and n1≠n2.

Preferably, more groups of orthogonal cover code sequences may begenerated according to processes similar to those in the steps S130 andS140 by changing the displacement of the cyclic shift of column vectors.

FIG. 2 shows an example diagram of four groups of orthogonal cover codesequences C₁ to C₄ generated according to the present invention. In thisexample, there are totally generated four groups of orthogonal covercode sequences, with each group of orthogonal cover code sequencesincluding four orthogonal sequences and the length of each orthogonalsequence being four. In this example, the generated orthogonal covercode sequences are Walsh sequences and the displacement of the cyclicshift processing of column vectors p=2.

FIG. 3 shows a flow chart of an orthogonal cover code mapping methodaccording to an embodiment of the present invention.

Firstly, in step S310, multiple groups of orthogonal cover codesequences are generated according to the orthogonal cover codegeneration method shown in FIG. 1, where the multiple groups oforthogonal cover code sequences include at least the first to fourthgroups of orthogonal cover code sequences.

Finally, in step S320, pilot sequences are spread with the multiplegroups of orthogonal cover code sequences according to a predeterminedmapping rule.

Preferably, in the spreading step, the orthogonal cover code sequencesare subjected to mapping processing in one or both of time and frequencydomains.

Preferably, the mapping rule is intended to reduce a variation range oftransmission power of the pilot sequences, or guarantee orthogonality ofthe pilot sequences in specific time-frequency two-dimensionalresources.

Preferably, in the spreading step, the multiple groups of orthogonalcover code sequences are made to be alternately present in thetime-frequency resources corresponding to the pilot sequences ofFrequency Division Multiplexing and/or Code Division Multiplexing inturn.

Preferably, in the spreading step, the multiple groups of orthogonalcover code sequences are made to be alternately present in thetime-frequency resources corresponding to the pilot sequences ofFrequency Division Multiplexing and/or Code Division Multiplexing inturn in one of the following orders: (C₁, C₂, . . . , C_(K−1), C_(K)),(C₂, C₃, . . . , C_(K), C₁), . . . (C_(K), C₁, . . . , C_(K−2),C_(K−1)); (C_(K), C_(K−1), . . . , C₂, C₁), (C_(K−1), C_(K−2), . . . ,C₁, C_(K)), . . . , (C₁, C_(K), . . . , C₃, C₂), where K is the numberof the multiple groups of orthogonal cover code sequences.

Preferably, in the spreading step, a mapping order of the multiplegroups of orthogonal cover code sequences in a first group of frequencydomain resources of Code Division Multiplexing is made to be differentfrom that in a second group of frequency domain resources of CodeDivision Multiplexing.

Preferably, in the spreading step, the multiple groups of orthogonalcover code sequences are made to be alternately present in the adjacentfirst and second groups of frequency domain resources of Code DivisionMultiplexing in turn.

Preferably, in the spreading step, Demodulation Reference Signals(DMRSs) of different data transmission layers of Code DivisionMultiplexing corresponding to two and four pilot symbols in the timedomain are made to be mutually orthogonal, and the DMRSs of differentdata transmission layers of Code Division Multiplexing corresponding tofour sub-carriers in the frequency domain are also made to be mutuallyorthogonal. Further preferably, in the spreading step, the DMRSs ofdifferent data transmission layers of Code Division Multiplexingcorresponding to two adjacent pilot symbols in the time domain and twoadjacent sub-carriers in the frequency domain are made to be mutuallyorthogonal.

Preferably, in the spreading step, each physical resource block is madeto contain at least the multiple groups of orthogonal cover codesequences.

The orthogonal cover code mapping method according to the embodiment ofthe present invention is to be described in combination with the figuresin detail as follows by taking an LTE-A Rel-10 system and 4 groups oforthogonal cover code sequences as an example. However, the skilled inthe art should be clear that the present invention is not limited to theexample described in the following.

FIG. 4 shows a schematic view of downlink DMRSs in the Rel-10 system. Ifthe data flow is 1 or 2, in each sub-frame of the LTE-A system, thepilot occupies 12 sub-carriers (Resource Element, RE) in the physicalresource blocks (PRBs) of the sixth and seventh OFDM symbols and thethirteenth and fourteenth OFDM symbols. The pilots of the first layerand the second layer occupy the same PRB and they are distinguished byan orthogonal cover code of a length of 2. If the data flow is >2, theDMRSs occupy extra 12 REs for transmitting the DMRSs of the third layerand the fourth layer. The pilots of the third layer and the fourth layeroccupy the same PRB and they are distinguished by an orthogonal covercode of a length of 2. If the data flow is >4, the number of the REsoccupied by the DMRSs dose not change and is still 24. Each data flowmay be distinguished in the manner of the code division multiplexing(CDM) and/or the frequency division multiplexing (FDM). One of thefeasible multiplexing manners is shown in FIG. 4. The first, second,fifth and seventh layers are multiplexed in the manner of CDM and aredistinguished by an orthogonal cover code of a length of 4. Thetime-frequency resources occupied are represented by the dark grids inthe figure, which are referred to as CDM group 1 for short. The third,fourth, sixth and eighth layers are multiplexed in the manner of CDM andare distinguished by an orthogonal cover code of a length of 4. Thetime-frequency resources occupied are represented by the grids withtwills in the figure, which are referred to as CDM group 2 for short.Moreover, the first, second, fifth and seventh layers and the third,fourth, sixth and eighth layers are multiplexed in the manner of FDM.

FIG. 5 shows a schematic view of mapping the four groups of orthogonalcover code sequences generated according to the present invention intothe downlink DMRS resources in the Rel-10 system. It can be seen fromthe figure that the orthogonal cover code sequences are spread in thetime domain. That is to say, the DMRSs corresponding to the samesub-carrier on the sixth, seventh, thirteenth and fourteenth OFDMsymbols form a spreading code of a length of 4. For the time-frequencyresource corresponding to CDM group 1, the generated four groups oforthogonal cover code sequences are mapped sequentially in turn in theorder of C₁, C₂, C₃ and C₄, so as to guarantee that all the orthogonalcover code sequences are included as much as possible in the entirefrequency band corresponding to CDM group 1. For the time-frequencyresource corresponding to CDM group 2, the generated four groups oforthogonal cover code sequences are mapped sequentially in turn in theorder of C₄, C₃, C₂ and C₁, so as to guarantee that all the orthogonalcover code sequences are included as much as possible in the entirefrequency band corresponding to CDM group 2. The corresponding DMRSresources in each PRB, including CDM group 1 and CDM group 2, all inturn include all the four groups of orthogonal cover code sequences. Forexample, in the first PRB, all the four groups of orthogonal cover codesequences are included in the (k)th, (k+1)th, (k+5)th and (k+6)thsub-carriers. Therefore, the effect of randomizing pilot sequences isachieved and the peak power of the sending signal is effectivelyreduced.

FIG. 6 shows a schematic view of power distribution of mapping thepre-encoded four groups of orthogonal cover code sequences generatedaccording to the present invention onto a first sending antenna. It canbe seen from the figure that if all the row vectors in the pre-encodingmatrix are 1, after the column vectors matrixes of the 4 groups oforthogonal cover code sequences C₁˜C₄ are respectively multiplied by therow vectors of the pre-encoding matrix and the products are respectivelyadded, on the (k)th sub-carrier, corresponding DMRSs of the first,second, eighth and ninth OFDM symbols are respectively 4, 0, 0 and 0; onthe (k+1)th sub-carrier, corresponding DMRSs of the first, second,eighth and ninth OFDM symbols are respectively 0, 0, 4 and 0; on the(k+5)th sub-carrier, corresponding DMRSs of the first, second, eighthand ninth OFDM symbols are respectively 0, 0, 0 and 4; and on the(k+6)th sub-carrier, corresponding DMRSs of the first, second, eighthand ninth OFDM symbols are respectively 0, 4, 0 and 0. It is notdifficult to see that the power of the DMRSs is uniformly distributed onthe four OFDM symbols, so as to avoid the problem of imbalanced power.

FIG. 7 shows a schematic view of the orthogonality in time-frequencytwo-dimensions according to the mapping method of the present invention.The orthogonal cover code sequences are spread in the time domain, andthe four pilot symbols in each sub-frame respectively correspond to fourcolumn vectors of the generated orthogonal cover code sequences. If thelength of spreading is 2, the orthogonal cover code sequences mapped inthis way also guarantee that the sequences corresponding to two pilotsymbols in each sub-frame are orthogonal. Moreover, the sequencescorresponding to adjacent four sub-carriers in each pilot symbol alsosatisfy the orthogonality of a length of 4 in the frequency domain.Furthermore, on two adjacent sub-carriers within a same CDM group, thecorresponding DMRSs of adjacent two OFDM symbols also form a spreadingcode of a length of 4, i.e. the orthogonality is provided in thetime-frequency two dimensions. For example, for CDM group 1, on the(k+1)th and (k+6)th sub-carriers, corresponding DMRSs of the first andsecond OFDM symbols also form mutually orthogonal spreading codes of alength of 4.

Although, in the above, the orthogonal cover code generation method andorthogonal cover code mapping method according to embodiments of thepresent invention are described in detail in conjunction with theaccompanying drawings, the skilled in the art should understand that theflow charts shown in FIGS. 1 and 3 are only exemplary, and the flow ofthe methods shown in FIGS. 1 and 3 may be correspondingly modifiedaccording to practical applications and specific requirements. Forexample, the performing order of some steps in the methods shown inFIGS. 1 and 3 may be adjusted or some processing steps may be omitted oradded as required.

The orthogonal cover code generation apparatus and orthogonal cover codemapping apparatus according to embodiments of the present invention areto be described in conjunction with the accompanying drawings asfollows.

FIG. 8 shows a structural block diagram of an orthogonal cover codegeneration apparatus 800 according to an embodiment of the presentinvention, where only the parts that are closely associated with thepresent invention are shown for the sake of simplicity and clarity. Inthe orthogonal cover code generation apparatus 800, the orthogonal covercode generation method described above with reference to FIG. 1 can beperformed.

As shown in FIG. 8, the orthogonal cover code generation apparatus 800may include a first orthogonal cover code sequence group generationmeans 810, a second orthogonal cover code sequence group generationmeans 820, a third orthogonal cover code sequence group generation means830 and a fourth orthogonal cover code sequence group generation means840.

In the orthogonal cover code generation apparatus 800, the firstorthogonal cover code sequence group generation means 810 may be usedfor generating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, where n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2.

The second orthogonal cover code sequence group generation means 820 maybe used for performing column mirroring on the first group of orthogonalcover code sequences, so as to generate a second group of orthogonalcover code sequences C₂.

The third orthogonal cover code sequence group generation means 830 maybe used for performing cyclic shift processing of column vectors on thefirst group of orthogonal cover code sequences, so as to generate athird group of orthogonal cover code sequences C₃.

The fourth orthogonal cover code sequence group generation means 840 maybe used for performing column mirroring on the third group of orthogonalcover code sequences, so as to generate a fourth group of orthogonalcover code sequences C₄.

Since the specific and/or optional processing procedures of eachcomponent of the orthogonal cover code generation apparatus 800 aredescribed in the above with reference to the flow chart of the method,the operation and the processing procedures of these components will notbe described in detail any more to avoid repetition.

It should be illustrated that the structure of the orthogonal cover codegeneration apparatus 800 shown in FIG. 8 is only exemplary, and theskilled in the art may modify the structural block diagram shown in FIG.8 as required.

FIG. 9 shows a structural block diagram of an orthogonal cover codemapping apparatus 900 according to an embodiment of the presentinvention, where only the parts that are closely associated with thepresent invention are shown for the sake of simplicity and clarity. Inthe orthogonal cover code mapping apparatus 900, the orthogonal covercode mapping method described above with reference to FIG. 3 can beperformed.

As shown in FIG. 9, the orthogonal cover code mapping apparatus 900 mayinclude an orthogonal cover code generation apparatus 910 and aspreading apparatus 920.

In the orthogonal cover code mapping apparatus 900, the orthogonal covercode generation apparatus 910 may be composed of an orthogonal covercode generation apparatus as shown in FIG. 8 for generating multiplegroups of orthogonal cover code sequences, where the multiple groups oforthogonal cover code sequences include at least the first to fourthgroups of orthogonal cover code sequences.

The spreading means 920 may be used for spreading pilot sequences withthe multiple groups of orthogonal cover code sequences according to apredetermined mapping rule.

Since the specific and/or optional processing procedures of eachcomponent of the orthogonal cover code mapping apparatus 900 aredescribed in the above with reference to the flow chart of the method,the operation and the processing procedures of these components will notbe described in detail any more to avoid repetition.

It should be illustrated that the structure of the orthogonal cover codemapping apparatus 900 shown in FIG. 9 is only exemplary, and the skilledin the art may modify the structural block diagram shown in FIG. 9 asrequired.

FIG. 10 shows a structural block diagram of a wireless communicationsystem 1000 according to an embodiment of the present invention. Asshown in FIG. 10, the wireless communication system 1000 may include atransmission apparatus 1010 and a reception apparatus 1020, where thetransmission apparatus 1010 may include the above mentioned orthogonalcover code mapping apparatus 900 and the reception apparatus 1020 mayinclude a reception means 1030 for receiving the spread pilot sequencesfrom the transmission apparatus 1010.

FIG. 11 shows a structural block diagram of a base station 1100according to an embodiment of the present invention. As shown in FIG.11, the base station 1100 may include the above mentioned orthogonalcover code generation apparatus 800.

FIG. 12 shows a structural block diagram of a mobile station 1200according to an embodiment of the present invention. As shown in FIG.12, the mobile station 1200 may include the above mentioned orthogonalcover code generation apparatus 800.

It is obvious that each operation procedure of the above mentionedmethods according to the present invention may be performed in themanner of a computer executable program stored in a machine-readablestorage medium.

Moreover, the object of the present invention may also be achieved inthe following manner, i.e. a storage medium which has the abovementioned executable program code stored therein is directly orindirectly provided to a system or device, and a computer or a centralprocessing unit (CPU) in the system or device reads out and executes theabove mentioned program code. In this case, the implementation of thepresent invention is not limited to a program and the program may be inany form such as an object program, a program executed by an interpreteror a script program provided to an operating system or the like, as longas the system or device has the function to execute the program.

These machine-readable storage media mentioned above include but notlimited to various memories and storage units, semiconductor devices,disk units such as optical disks, magnetic disks and magneto-opticaldisks, other media suitable to store information and so on.

Moreover, the present invention may also be achieved in the followingmanner, i.e. a computer is connected to a corresponding web site on theinternet and computer program codes according to the present inventionare downloaded and installed in the computer and are executed therein.

It is obvious that each of the components or steps in the devices andmethods of the present invention may be decomposed and/or may berecombined. These decompositions and/or re-combinations should beregarded as equivalent schemes of the present invention. Moreover, thesteps carrying out the series of processes mentioned above may benaturally performed chronically in an order of description but notnecessarily. Some of the steps may be carried out in parallel orindependently from each other.

Although the embodiments of the present invention are described indetail in conjunction with the accompanying drawings, it should beappreciated that the above mentioned embodiments are only forillustration of the present invention and do not limit the presentinvention. For the skilled in the art, various modifications andalternations may be made to the above mentioned implementations withoutdeparting the essential and scope of the present invention. Therefore,the scope of the present invention is only defined by the appendedclaims and their equivalent meanings.

Although illustrative embodiments have been described herein, it shouldbe understood that various other changes, replacements and modificationsmay be affected therein by one skilled in the art without departing fromthe scope or spirit of the invention. Furthermore, the terms“comprises,” “comprising,” or any other variation thereof are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that comprises the element.

According to various embodiments, the present disclosure provide thefollowing solutions:

1. An orthogonal cover code generation apparatus, comprising:

a first orthogonal cover code sequence group generation means forgenerating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, wherein n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2;

a second orthogonal cover code sequence group generation means forperforming column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂;

a third orthogonal cover code sequence group generation means forperforming cyclic shift processing of column vectors on the first groupof orthogonal cover code sequences, so as to generate a third group oforthogonal cover code sequences C₃; and

a fourth orthogonal cover code sequence group generation means forperforming column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄.

2. The orthogonal cover code generation apparatus according to solution1, wherein the first group of orthogonal cover code sequences are WalshCode sequences or Flourier Transform sequences.

3. The orthogonal cover code generation apparatus according to solution1, wherein the first to fourth groups of orthogonal cover code sequencesare respectively represented by C_(i)=[C_(n, i)(1), C_(n, i)(2), . . .C_(n, i)(M)], wherein i is an index of each group of orthogonal covercode sequences, the first to fourth groups of orthogonal cover codesequences satisfy that the column vectors of each group of orthogonalcover code sequences have different column numbers in a matrix of eachgroup of orthogonal cover code sequences, and {tilde over (C)}_(n,k)^(l)=[C_(n,2k 1)(2l−1), C_(n,2k 1)(2l), C_(n,2k)(2l−1), C_(n,2k)(2l)]composed of two adjacent groups of orthogonal cover code sequencesC_(2k−1) and C_(2k) satisfy that {tilde over (C)}_(n1,k) ^(l) and {tildeover (C)}_(n2,k) ^(l) are mutually orthogonal, wherein k=1 or 2, 1 is aninteger satisfying 1≦l≦M/2, n1 is an integer satisfying 1≦l≦N, n2 is aninteger satisfying 1≦n223 N, and n1≠n2.

4. An orthogonal cover code mapping apparatus, comprising:

the orthogonal cover code generation apparatus according to solution 1for generating multiple groups of orthogonal cover code sequences,wherein the multiple groups of orthogonal cover code sequences compriseat least the first to fourth groups of orthogonal cover code sequences;and

a spreading means for spreading pilot sequences with the multiple groupsof orthogonal cover code sequences according to a predetermined mappingrule.

5. The orthogonal cover code mapping apparatus according to solution 4,wherein the spreading means performs mapping on the orthogonal covercode sequences in one or both of time and frequency domains.

6. The orthogonal cover code mapping apparatus according to solution 5,wherein the mapping rule is intended to reduce a variation range oftransmission power of the pilot sequences, or guarantee orthogonality ofthe pilot sequences in specific time-frequency two-dimensionalresources.

7. The orthogonal cover code mapping apparatus according to solution 5,wherein the spreading means makes the multiple groups of orthogonalcover code sequences alternately present in the time-frequency resourcescorresponding to the pilot sequences of Frequency Division Multiplexingand/or Code Division Multiplexing in turn.

8. The orthogonal cover code mapping apparatus according to solution 7,wherein the spreading means makes the multiple groups of orthogonalcover code sequences alternately present in the time-frequency resourcescorresponding to the pilot sequences of Frequency Division Multiplexingand/or Code Division Multiplexing in turn in one of the followingorders: (C₁, C₂, . . . , C_(K−1), C_(K)), (C₂, C₃, . . . , C_(K), C₁), .. . (C_(K), C₁, . . . , C_(K−2), C_(K−1)); (C_(K), C_(K−1), . . . , C₂,C₁), (C_(K−1), C_(K−2), . . . , C₁, C_(K)), . . . , (C₁, C_(K), . . . ,C₃, C₂), wherein K is the number of the multiple groups of orthogonalcover code sequences.

9. The orthogonal cover code mapping apparatus according to solution 7,wherein the spreading means makes a mapping order of the multiple groupsof orthogonal cover code sequences in a first group of frequency domainresources of Code Division Multiplexing different from that in a secondgroup of frequency domain resources of Code Division Multiplexing.

10. The orthogonal cover code mapping apparatus according to solution 7,wherein the spreading means makes the multiple groups of orthogonalcover code sequences alternately present in the adjacent first andsecond groups of frequency domain resources of Code DivisionMultiplexing in turn.

11. The orthogonal cover code mapping apparatus according to solution 7,wherein the spreading means makes Demodulation Reference Signals (DMRSs)of different data transmission layers of Code Division Multiplexingcorresponding to two and four pilot symbols in the time domain mutuallyorthogonal, and also makes the DMRSs of different data transmissionlayers of Code Division Multiplexing corresponding to four sub-carriersin the frequency domain mutually orthogonal.

12. The orthogonal cover code mapping apparatus according to solution11, wherein the spreading means makes the DMRSs of different datatransmission layers of Code Division Multiplexing corresponding to twoadjacent pilot symbols in the time domain and two adjacent sub-carriersin the frequency domain mutually orthogonal.

13. The orthogonal cover code mapping apparatus according to solution 6,wherein the spreading means makes each physical resource block containat least the multiple groups of orthogonal cover code sequences.

14. An orthogonal cover code generation method, comprising:

a first orthogonal cover code sequence group generation step ofgenerating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, wherein n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2;

a second orthogonal cover code sequence group generation step ofperforming column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂;

a third orthogonal cover code sequence group generation step ofperforming cyclic shift processing of column vectors on the first groupof orthogonal cover code sequences, so as to generate a third group oforthogonal cover code sequences C₃; and

a fourth orthogonal cover code sequence group generation step ofperforming column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄.

15. A wireless communication system comprising:

a transmission apparatus and a reception apparatus,

wherein the transmission apparatus includes:

a first orthogonal cover code sequence group generation means forgenerating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2J, 1)(2m−1),C_(2j, 1)(2m)] are also mutually orthogonal, wherein n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2;

a second orthogonal cover code sequence group generation means forperforming column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂;

a third orthogonal cover code sequence group generation means forperforming cyclic shift processing of column vectors on the first groupof orthogonal cover code sequences, so as to generate a third group oforthogonal cover code sequences C₃; and

a fourth orthogonal cover code sequence group generation means forperforming column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄, and

wherein the reception apparatus includes:

a reception means for receiving the spread pilot sequences from thetransmission apparatus.

16. A method in a wireless communication system including a transmissionapparatus and a reception apparatus, the method comprising:

at the transmission apparatus,

generating a first group of orthogonal cover code sequences C₁represented by a matrix of [C_(n, 1)(1), C_(n, 1)(2), . . .C_(n, 1)(M)], which satisfy that any adjacent truncated sub cover codesequences [C_(2j−1, 1)(2m−1), C_(2j−1, 1)(2m)] and [C_(2j, 1)(2m−1),C_(2J, 1)(2m)] are also mutually orthogonal, wherein n is an index of Northogonal cover code sequences included in the first group oforthogonal cover code sequences, M is a spreading factor of theorthogonal cover code sequence as a spreading sequence, N≦M, j is aninteger satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2;

performing column mirroring on the first group of orthogonal cover codesequences, so as to generate a second group of orthogonal cover codesequences C₂;

performing cyclic shift processing of column vectors on the first groupof orthogonal cover code sequences, so as to generate a third group oforthogonal cover code sequences C₃; and

performing column mirroring on the third group of orthogonal cover codesequences, so as to generate a fourth group of orthogonal cover codesequences C₄, and

at the reception apparatus,

receiving the spread pilot sequences from the transmission apparatus.

What is claimed is:
 1. A base station which performs Multiple InputMultiple Output (MIMO) transmission, comprising: a processor configuredto generate reference signals by spreading with four groups oforthogonal code sequences, each group of orthogonal code sequencesincluding four orthogonal sequences, wherein the orthogonal codesequences correspond to transmission layers and each of the orthogonalcode sequences has a length of four, and a transmit circuit configuredto transmit the reference signals to a mobile station, wherein the fourgroups includes a first group in which the orthogonal code sequences areWalsh code sequences, a second group in which the orthogonal codesequences are represented by mirroring of the orthogonal code sequencesin the first group, a third group in which the orthogonal code sequencesare represented by cyclic shifts of the orthogonal code sequences in thefirst group, and a fourth group in which the orthogonal code sequencesare represented by mirroring of the orthogonal code sequences in thethird group, and wherein the first and the third groups of theorthogonal code sequences are to be mapped to the adjacent sub-carriersin the frequency domain.
 2. The base station according to claim 1,Wherein each of the orthogonal code sequences corresponds to one of thetransmission layer so that the transmission layers are distinguished bythe orthogonal code sequences.
 3. A mobile station which performs acommunication with a base station using Multiple input Multiple Output(MIMO), comprising: a receive circuit configured to receive from thebase station reference signals-spread by four groups of orthogonal codesequences, each group of orthogonal code sequences including fourorthogonal sequences, Wherein the orthogonal code sequences correspondto transmission layers and each of the orthogonal code sequences has alength of four, wherein the four groups includes a first group in whichthe orthogonal code sequences are Walsh code sequences, a second groupin which the orthogonal code sequences are represented by mirroring ofthe orthogonal code sequences in the first group, a third group in whichthe orthogonal code sequences are represented by cyclic shifts of theorthogonal code sequences in the first group, and a fourth group inwhich the orthogonal code sequences are represented by mirroring of theorthogonal code sequences in the third group, and wherein the first andthe third groups of the orthogonal code sequences are to be mapped tothe adjacent sub-carriers in the frequency domain.
 4. The mobile stationaccording to claim 3, further comprising a processor circuit configuredto despread the received reference signals.
 5. The mobile stationaccording to claim 4, wherein each of the orthogonal code sequencescorresponds to one of the transmission layer so that the transmissionlayers are distinguished by the orthogonal code sequences.
 6. Acommunication system, comprising: a base station and a mobile stationwhich perform communication using Multiple Input Multiple Output (MIMO);wherein the base station includes, a processor configured to generatereference signals by spreading with four groups of orthogonal codesequences, each group of orthogonal code sequences including fourorthogonal sequences, wherein the orthogonal code sequences correspondto transmission layers and each of the orthogonal code sequences has alength of four, and a transmit circuit configured to transmit thereference signals to a mobile station, and wherein the mobile stationincludes, a receive circuit configured to receive reference signalstransmitted from the base station, and wherein the four groups includesa first group in which the orthogonal code sequences are Walsh codesequences, a second group in which the orthogonal code sequences arerepresented by mirroring of the orthogonal code sequences in the firstgroup, a third group in which the orthogonal code sequences arerepresented by cyclic shifts of the orthogonal code sequences in thefirst group, and a fourth group in which the orthogonal code sequencesare represented by mirroring of the orthogonal code sequences in thethird group, and wherein the first and the third groups of theorthogonal code sequences are to be mapped to the adjacent sub-carriersin the frequency domain.